Methods and systems for magnetic media servo writing

1. A method comprising:

generating a first magnetic field component in a recording layer of a magnetic tape medium;

generating a second magnetic field component in the recording layer of the magnetic tape medium, the second magnetic field component oriented substantially opposite the first magnetic field component;

writing a servo pattern onto the recording layer of the magnetic tape medium;

generating a servo signal by reading the servo pattern from the recording layer of the magnetic tape medium;

determining an asymmetry in the servo signal; and

controlling a magnitude of the second magnetic field component based on the asymmetry.

2. The method of claim 1 , wherein determining an asymmetry in the servo signal comprises comparing a positive peak amplitude in the servo signal to a negative peak amplitude in the servo signal.

3. The method of claim 2 , wherein controlling a magnitude of the second field component comprises controlling the magnitude to reduce the asymmetry in a perpendicular bias of the recording layer.

4. The method of claim 1 , wherein generating the first field component comprises generating a fixed field component with a fixed-field magnetic head, the fixed field component oriented substantially perpendicular to the recording layer.

5. The method of claim 4 , wherein generating the second field component comprises generating a variable field component with an electromagnetic head, the variable field component oriented substantially perpendicular to the recording layer.

6. The method of claim 5 , wherein controlling a magnitude of the second field component comprises adjusting a current supply to the electromagnetic head to reduce or minimize perpendicular bias in the recording layer.

7. A magnetic tape medium system comprising:

first and second magnetic heads positioned along the magnetic tape medium, the first and second magnetic heads configured to generate first and second substantially opposite magnetic field components in a recording layer of the magnetic tape medium;

a write head positioned along the magnetic tape medium, the write head configured to write a servo pattern onto the recording layer of the magnetic tape medium;

a read head positioned along the magnetic tape medium, the read head configured to generate a servo signal by reading the servo pattern; and

a controller connected to the read head and the second magnetic head, the controller configured to control a magnitude of the second magnetic field component based on an asymmetry of the servo signal.

8. The magnetic tape medium system of claim 7 , further comprising a soft magnetic underlayer disposed for flux return, wherein the recording layer is configured for perpendicular recording.

9. The magnetic tape medium system of claim 8 , wherein the recording layer comprises one or more of barium ferrite, strontium ferrite and cobalt ferrite.

10. The magnetic tape medium system of claim 8 , wherein the first and second field components are oriented substantially perpendicular to the recording layer.

11. The magnetic tape medium system of claim 10 , wherein controlling a magnitude of the second field component comprises controlling the magnitude to reduce or minimize perpendicular bias in the recording layer.

12. A system comprising:

first and second magnetic heads positioned along a magnetic tape medium, the first and second magnetic heads configured to generate first and second substantially opposite magnetic field components in a recording layer of the magnetic tape medium;

a write head positioned along the magnetic tape medium, the write head configured to write a servo pattern onto the recording layer of the magnetic tape medium;

a read head positioned along the magnetic tape medium, the read head configured to generate a servo signal by reading the servo pattern; and

a controller connected to the read head and the second magnetic head, the controller configured to control a magnitude of the second magnetic field component based on an asymmetry of the servo signal.

13. The system of claim 12 , wherein the magnetic tape medium comprises a layered magnetic recording material having a perpendicular recording layer and a soft magnetic underlayer.

14. The system of claim 13 , wherein the first and second magnetic field components are oriented substantially perpendicular to the perpendicular recording layer.

15. The system of claim 13 , wherein the perpendicular recording layer comprises one or more of barium ferrite, strontium ferrite or cobalt ferrite.

16. The system of claim 12 , wherein the first and second magnetic heads are spaced apart from one another along the magnetic tape medium.

17. The system of claim 12 , wherein the second magnetic head comprises an electromagnetic head configured to generate perpendicular bias in the recording layer.

18. The system of claim 17 , wherein the controller is configured to control the magnitude of the second magnetic field component by adjusting a coil current to the electromagnetic head.

19. The system of claim 17 , wherein the controller is configured to reduce or minimize the asymmetry of the servo signal by increasing or decreasing the coil current.

20. The system of claim 17 , wherein the controller is configured to reduce or minimize perpendicular bias in the magnetic tape medium by increasing or decreasing the coil current.